1. FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for measuring hardness of an ultraviolet curing transformation agent comprising a stain which is applied on a work and dried with an optical device.
2. PRIOR ART
Ultraviolet curing transformation agents have been widely used because they can be applied to un-heat-treatable materials and enable high-speed printing. The ultraviolet curing transformation agents are now utilized in various industrial fields, for example, general printed matter, compact discs, building materials, floor materials such as tiles, wall materials, resist for printed board, beverage cans and so on.
After printed on a material, the ultraviolet (UV) curing transformation agent is dried by a conveyor apparatus comprising an ultraviolet ray source such as a high-pressure mercury-vapor lamp or a metal halide lamp while the printing material is transferred. Alternatively, the UV curing transformation agent is dried by an apparatus comprising a light source for spotlighting. The most significant point for the use of the transformation agents is adjusting the intensity of ultraviolet ray and the ultraviolet ray radiation time for curing (drying) the transformation agent in accordance with the types of transformation agents.
Various means for measuring the hardness of the ultraviolet curing transformation agents have been proposed. For example, the hardness is measured by a taping test, a cross-cutting test a dye immersing method, or examined by visual examination, tactile impression and so on.
Further, in order to measure the precise hardness, there are nuclear magnetic resonance (NMR), infrared spectrophotometry, and a method for measuring the extension of transformation agents, but actually these are employed only in researches.
Furthermore, there has been proposed a method for determining the hardness from the change in electric resistance or the transformation agent as a method for measuring the hardness of the transparent ultraviolet curing transformation agent. The apparatus for carrying out this method comprises a light source device, and electrodes provided at both sides of the ultraviolet curing transformation agent applied on an insulator and connected each other through a power supply and a measuring device for measuring the electric conductivity.
Accordingly, as the transformation agent is gradually cured by the ultraviolet ray irradiation, the electric conductivity between both electrodes is decreased. Then, the hardness of the transformation agent can be measured by the electric conductivity measuring device. It is clear from the concurrent measurement with the use of dial gauge that the decrease of the electric conductivity is proportional to the hardness of the transformation agent. That is, the hardness (dryness) is determined by measuring how much the dial gauge is suck in the transformation agent.
However, there still exist the following problems in the above-described method for measuring the hardness of the ultraviolet curing transformation agent.
(1) Because the visual examination and tactile impression depend upon operators and some kinds of standards are never established, it is hard to prevent the inconvenient phenomenon in printing process such as crystallization and back-trapping.
(2) The NMR and the infrared spectrophotometry enable the accurate measurement; however, in view of the prompt measurement, the location of the device and the environment of the device, it is difficult to use these methods in practice.
(3) In the case of ultraviolet curing transformation agent comprising a stain, the stain absorbs the ultraviolet ray having a predetermined wavelength and the electric conductivity is kept high and not varied in accordance with the hardness of the UV curing transformation agent while the UV ray irradiates. Therefore, the determination of the hardness of the UV curing transformation agent based on the change in electric conductivity is impossible.